The present disclosure relates to detection methods in oral health care.
With the widespread use of fluoride, the prevalence of dental caries has been considerably reduced. Nonetheless, the development of a non-invasive, non-contact technique that can detect and monitor early demineralization or small carious lesions on or beneath the enamel, dentin, root surface or around the margins of dental restorations, is essential for the clinical management of this problem.
In dentistry, the aim of recent scientific research has been the use of laser fluorescence for detection of tooth demineralization and dental caries (e.g. enamel and/or root), dental deposits, and dental calculus and quantitative analysis of lesion depth and size, as well as the mineral composition of the enamel [M. L. Sinyaeva, Ad. A. Mamedov, S. Yu. Vasilchenko, A. I. Volkova, and V. B. Loschenov, 2003, “Fluorescence Diagnostics in Dentistry”, Laser Physics, 14, No. 8, 2004, pp. 1132-1140]. These principles have been used to develop a number of fluorescence-based technologies, such as QLF™ and DIAGNOdent™ diagnostic devices.
UV radiation (488 nm) has been used to examine dental enamel [Susan M. Higham, Neil Pender, Elbert de Josselin de Jong, and Philip W. Smith, 2009. Journal of Applied Physics 105, 102048, R. Hibst and R. Paulus, Proc. SPIE 3593, 141 (1999)]. The studies showed that autofluorescence of healthy enamel were peaked at a wavelength of 533 nm, whereas the autofluorescence of carious tissue was red-shifted by 40 nm. It was also demonstrated that the autofluorescence intensity of carious zones was an order-of-magnitude lower than the autofluorescence intensity of a healthy tooth in spite of the fact that the absorbance of the carious zone at the excitation wavelength was significantly higher.
The reduction in fluorescence when enamel demineralizes or a carious lesion has developed has been attributed to the increase in porosity of carious lesions when compared with sound enamel. There is an associated uptake of water and decrease in the refractive index of the lesion resulting in increased scattering and a decrease in light-path length, absorption, and autofluorescence [H. Bjelkhagan, F. Sundström, B. Angmar-M{hacek over (a)}nsson, and H. Ryder, Swed Dent. J. 6, 1982].
At long excitation wavelengths, the autofluorescence intensity of a carious cavity can be higher than the autofluorescence intensity of healthy tissue [R. Hibst et al.]. For excitation wavelengths of 640 or 655 nm, the integral (at wavelengths greater than 680 nm) autofluorescence intensity of a carious lesion could be approximately one order-of-magnitude greater than the corresponding integral autofluorescence intensity of healthy enamel. There is some indication that the induced fluorescence with these wavelengths results from the excitation of fluorescent fluorophores from bacterial metabolites. These fluorophores are thought to originate from porphyrins found in some bacterial species [S. M. Higham et al.].
More recently, a new system has been developed based on the combination of laser induced fluorescence and photothermal radiometry. The system, commercially available as The Canary Dental Caries Detection System™, which examines luminescence and photothermal effect (PTR-LUM) of laser light on a tooth, as described in US Patent Application No. 2007/0021670, titled “Method and Apparatus Using Infrared Photothermal Radiometry (PTR) and Modulated Laser Luminescence (LUM) for Diagnostics of Defects in Teeth”, filed Jul. 18, 2006. The laser is non-invasive and can detect tooth decay a fraction of a millimeter in size and up to five millimeters below a tooth's surface. When pulses of laser light are focused on a tooth, the tooth glows and releases heat. By analyzing the emitted light and heat signatures from the tooth, very accurate information about the tooth's condition can be obtained including signs of early demineralization (lesions) of enamel [Nicolaides, L, Mandelis, A., Abrams, S. H., “Novel Dental Dynamic Depth Profilometric Imaging using Simultaneous Frequency Domain Infrared Photothermal Radiometry and Laser Luminescence”, Journal of Biomedical Optics, 2000, January, Volume 5, #1, pages 31-39, Jeon, R. J., Han, C., Mandelis, A., Sanchez, V Abrams, S. H “Non-intrusive, Non-contacting Frequency-Domain Photothermal Radiometry and Luminescence Depth Profilometry of Carious and Artificial Sub-surface Lesions in Human Teeth,” Journal of Biomedical Optics 2004, July-August, 9, #4, 809-81, Jeon R. J., Hellen A Matvienko A Mandelis A Abrams S. H Amaechi B. T., In vitro Detection and Quantification of Enamel and Root Caries Using Infrared Photothermal Radiometry and Modulated Luminescence. Journal of Biomedical Optics 13(3), 048803, 2008]. As a lesion grows, there is a corresponding change in the signal. As remineralization progresses, a signal reversal indicates an improvement in the condition of the tooth. By changing the frequency of the signal one can probe up to 5 mm below the tooth surface. Low frequency signals can penetrate the defects and lesions beneath the tooth surface.
One significant drawback with the aforementioned systems is the complex and expensive optical delivery systems that are typically needed. Moreover, some systems involve a handpiece that is optically coupled to a remote detector and laser source unit via an expensive fiber bundle assembly. This results in numerous drawbacks, including cost, complexity, and inconvenience of use due to the weight of the cables sheathing the fiber bundles.